the ground, and that lifted foot is then placed in
front of the grounded one, underneath the torso.

During this foot placement,the upper torso shifts
forward with the legs, evenlydistributing the COG
between the two legs
until it is ready to take
another step. Then, the
torso shifts forward
again until its COG is
centered on top of the
forward grounded
foot and the cycle is
repeated for the
opposite leg. What you
end up with is a biped
that knows how
to ‘walk the line,’
and an upper
torso that stays
considerably more
stable while
walking. Figure 7
is a 3D rendering of
the original

MicroRaptor robot
demonstrating the stepping
pattern of this gait.

There are a few pros and
cons to this method of walking.
Benefits include: a steadier upper
torso while walking; a lower
impact gait; and a longer stride.
The feet are brought completely
off of the ground when taking
steps, minimizing friction found
with standard ‘shuffle’ gaits
which cause the robot to veer
off course when walking
straight. For all of the benefits,
there are some inherent flaws
that come with both the gait
and the leg design.

The gait itself is considerably
harder to design and program,
given that the COG must be
accounted for more so on both
x and y due to the longer stride,
whereas a standard gait is
mostly just shifting the COG
from side to side. Even when
using the positional capture
features of the Dynamixel servos,
this is no easy task. The inline
stepping pattern trades the
forward back instability of a
standard walking gait for an
increased instability side to side.
Also, a higher COG is required to
properly ballast which leads to a

more top heavy bot. This top heavy nature side
to side instability can both be accounted and
compensated for through the use of an IMU and
balance engine; this is most certainly in my near
future plans for Hagetaka.

Conclusion

Figure 6

Next month, we will
cover the wiring and power
distribution scheme,
the onboard Gumstix
controller, remote
control setup, weapons,
supporting telepresence
electronics, the armor,
and scoring system.
To check out the
latest progress, visit
http://forums.
trossenrobotics.
com.

Until next
time ... SV

Parts List

Robotis Frame Components
www.trossenrobotics.com

• [14x] RX- 64 Dynamixel Actuators

• [2x] RX- 28 Dynamixel Actuators

• [12x] RX-64H Bearing Set

• [2x] RX-64T Thrust Bearing Set

• [4x] OF-64X Brackets

• [4x] OF-64FL Brackets

• [1x] OF-RX28T Thrust Bearing Set

• [1x] OF-RX28H Set

• [2x] OF-RX28S

Custom Brackets (patterns are
available at
www.servomagazine.com
with the June issue installment).